Built around 1465, this fortified tower house once served as the stronghold of the local Anglo-Norman nobility. The castle's strategic position allowed its inhabitants to oversee the surrounding farmland whilst maintaining defensive capabilities against potential raiders. Though now ruined, the structure still reveals the architectural ingenuity of late medieval Ireland, with its thick limestone walls and narrow window openings designed to withstand siege warfare.

The castle's history reflects the turbulent nature of Irish politics during the early modern period. Originally constructed by a branch of the Butler family, who held considerable power in the region, Ballynacooly changed hands several times over the centuries. During the Cromwellian conquest of Ireland in the 1650s, the castle suffered significant damage when Parliamentary forces attacked royalist strongholds throughout the country. The building never fully recovered from this assault, gradually falling into disrepair as newer, more comfortable manor houses became fashionable amongst the landed gentry.

Today, visitors can explore the atmospheric ruins, which include substantial portions of the tower's walls and the remnants of its vaulted chambers. The site offers insight into how these frontier fortresses functioned; the ground floor likely housed storage and livestock, whilst the upper floors contained the family's living quarters and defensive positions. Archaeological surveys have revealed evidence of earlier structures on the site, suggesting this location has been of strategic importance since at least the 13th century. The castle grounds are accessible to the public, though care should be taken when exploring the ruins due to uneven surfaces and loose masonry.